1. Field of the Invention
The present invention relates generally to systems for separating selected articles from a stream of articles, and more particularly, but not by way of limitation, to a system particularly suited for sorting recyclable materials such as different types of plastic containers and paper or cardboard products, including carrier board, from each other.
2. Description of the Prior Art
Environmental campaigns and recycling efforts in many areas have generated a substantial supply of recyclable waste paper and like materials. These materials need to be sorted before they can be recycled. For instance, plastic and glass articles need to be sorted from the stream itself and then further by plastic resin type, color, etc. Colored paper stock often needs to be separated from white stock, and cardboard and carrier board needs to be removed from newsprint. In addition, it is sometimes necessary or desirable to separate printed materials from blank materials. Further, separation processes such as screens designed to remove cardboard and plastic and metal containers from paper streams, often miss some of those materials, requiring additional separation steps. Unfortunately, sorting of waste paper and paperboard, etc. is still currently performed almost entirely by manual sorting. Manual sorting of such materials can be time consuming and expensive, which can render the use of recycled paper less economical than virgin paper material. This is even more apparent when so-called carrier board is present in the waste stream. So-called carrier board, commonly understood to be as the paperstock used in, e.g., cereal boxes, soda or beer can carriers, frozen food boxes, etc., must be sorted manually, as there is currently no effective automated method for doing do.
Numerous automated waste separation techniques are known. However, these techniques are generally designed for the recovery of metals, alloys, municipal waste, mixed recyclables and plastics. Paper (or, more generally, sheeted material) sorting presents unique problems that cannot be overcome by most prior art separation techniques. For instance, the relatively lightweight and flexible nature of paper presents unique problems when sorting is attempted. Indeed, these problems make it difficult to supply paper to a sorting sensor, especially not at a desirable feed rate (usually defined in terms of feet per minute (fpm), but sometimes also in terms of pieces or objects per minute (ppm) or tons per hour (tph)). Without higher speeds, automated sorting systems do not achieve efficiencies substantially greater than manual sorting. The problem is exacerbated where the waste stream includes paper and non-paper waste.
A number of different sorting systems have been proposed in the prior art for sorting various articles based upon the color of the articles or the characteristics of the reflected or transmitted electromagnetic radiation to which the article is exposed. Such systems have been utilized for sorting glass, plastic, paper, newsprint, fruit and other edible items, and the like. Similarly, a number of arrangements have been provided for carrying the articles through an inspection zone, and for exposing the articles to electromagnetic radiation and then collecting and analyzing the reflected and/or transmitted radiation.
For example, U.S. Pat. No. 4,131,540 to Husome et al. discloses a color sorting system wherein light is reflected off tomatoes and the reflected light is collected and analyzed as the tomatoes fly through an inspection zone.
U.S. Pat. No. 4,657,144 to Martin et al. discloses a system for removing foreign material from a stream of particulate matter such as tobacco as it cascades through an inspection zone.
U.S. Pat. No. 4,919,534 to Reed, discloses a system for determining the color of glass bottles, wherein the light energy is transmitted through the glass bottles.
U.S. Pat. No. 5,085,325 to Jones et al. discloses a system of a very common type wherein articles are examined as they are supported upon a moving conveyor belt.
U.S. Pat. No. 5,297,667 to Hoffman et al. discloses a system of utilizing two light sources and a camera to analyze articles as they fly through an inspection zone.
U.S. Pat. No. 5,314,072 to Frankel et al. discloses a system which analyzes the transmissive characteristics of articles which are exposed to x-ray fluorescence.
U.S. Pat. No. 5,318,172 to Kenny et al. discloses a system which distinguishes different types of plastic materials based upon their reflected electromagnetic radiation.
U.S. Pat. No. 5,333,739 to Stelte discloses another system which transmits light through articles, namely glass articles, and analyzes the transmitted light to determine color.
U.S. Pat. No. 5,443,164 to Walsh et al. discloses a plastic container sorting system which utilizes both transmitted electromagnetic energy and reflected electromagnetic energy to analyze and identify articles.
U.S. Pat. No. 5,675,416 to Campbell et al. discloses an apparatus which looks at the transmissive properties of articles to separate them based upon the material of the article.
U.S. Pat. No. 5,848,706 to Harris discloses a sorting apparatus which examines optical characteristics of the articles against a viewing background.
U.S. Pat. No. 5,966,217 to Roe et al. discloses a system for analyzing articles wherein reflected radiation is split into a plurality of streams which are then filtered and analyzed.
It has also been suggested to separate carrier board from a newspaper stream via a color-based identification system. However, this approach is not very effective or accurate since color is a secondary feature of these materials, not a fundamental characteristic.
In a relatively recent and unique approach, Doak et al., in U.S. Pat. No. 6,497,324, disclose a sorting system utilizing a multiplexer to allow a single analyzer unit to be used to analyze electromagnetic signals from each of a plurality of collector units. Although effective, the Doak et al. system requires the operation of complex and highly sensitive software and mechanical components, which can be difficult to maintain.
In addition, as noted above, another problem encountered by waste sorting systems is the identification and separation of carrier board and coated or waxed board material commonly used as, e.g., beverage cartons, cigarette cartons, etc. from other paper materials. More particularly, the separation of white or printed paper stock from an article stream can be accomplished by recently developed systems, leaving newsprint and carrier board in the article stream. Further separation to provide only newsprint in the stream, however, has proven problematic.
Thus, it is seen that although there have been many arrangements proposed for the examination of a stream of articles by analysis of reflected and/or transmitted electromagnetic radiation from the articles, there is a continuing need for improved systems, which may simplify the analytical mechanism and permit the identification of materials (such as carrier board) heretofore found difficult to process.